Frequently, an electrophotographic printing machine processes highlight or multicolor original documents to form copies thereof. In an electrophotographic printing machine, a photoconductive member is charged to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive member is thereafter selectively exposed in an imaging zone to a light source such as a raster output scanner. Exposure of the charged photoconductive member dissipates the charge thereon in the irradiated areas. This discharge records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document being reproduced. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted to the latent image from the carrier granules to form a toner image on the photoconductive member which is subsequently transferred to a copy sheet. The copy sheet is then heated to permanently affix the toner image thereto in the image configuration.
Multicolor electrophotographic printing is substantially identical to the foregoing process of black and white printing. However, rather than forming a single latent image on the photoconductive surface, successive latent images corresponding to different colors are recorded thereon. Each single color electrostatic latent image is developed with toner of a color complimentary thereto. This process is repeated a plurality of cycles for differently colored images and their respective complimentarily colored toner. Each single color toner image is transferred to the copy sheet in superimposed registration with the prior toner image. This creates a multilayered toner image on the copy sheet. Thereafter, the multilayered toner image is permanently affixed to the copy sheet creating a color copy.
In the area of multicolor electrophotographic printing, it is highly desirable to accurately control the charging characteristics of the photoconductive surface at all stages of the electrophotographic process in order to obtain reliable renditions of the original document. Other charging devices are utilized within the transfer and cleaning operations of the electrophotographic process and the power supplied to these devices, as well as any bias voltages applied to enhance development of the latent images, must be similarly controlled.
Heretofore, numerous power supply designs have been employed within electroreprographic machines to control the voltage level produced by the power supplies. The following disclosures may be relevant to various aspects of the present invention: